1. Field of Invention
The present invention relates to abrasive saw blades or cutting wheels and specifically to industrial saw blades of the type formed by a circular sheet metal drive core having one or more cutting members containing disbursed diamond dust secured around the drive core periphery.
2. Description of Prior Developments
Industrial saw blades referred to as the discontinuous rim or segmented type blade are well-known and currently in widespread use. This type of blade is made by mounting to a circular core a series of short arcuate abrasive cutting segments containing diamond powder disbursed in a metal matrix. These cutting segments are usually about two inches long and are ordinarily silver soldered, brazed or welded to the rim of a steel core which has been divided into a plurality of support sections having peripheral surfaces for supporting the cutting segments.
The support sections are separated by radially extending gullets which accommodate the large thermal stresses created by the frictional heating of the blade periphery during cutting operations as well as the large thermal stresses created during the mounting of the cutting segments on the blade core during manufacture. Segmented blades have been accepted by those industries that subject the blades to heavy duty use, such as the concrete, asphalt and masonry cutting industries where rough abrasive cutting is commonplace.
For such rigorous applications, it is common to continuously flush the cutting area during the cutting operation with a fluid coolant in order to keep the blade as cool as possible. The coolant also serves to flush loose rock-like material, spent abrasive and the like from the cutting site, all of which in combination with the coolant is generally referred to in the art and throughout the description of the present invention as "swarf".
Even though construction of segmented blades has been developed to a high point of perfection, blades must commonly be replaced whenever the swarf erodes the steel drive core adjacent the junction of the cutting segments with the core. This erosion occurs radially inwardly of the cutting segments around the weld line between the segments and the core and is commonly referred to as "undercutting".
Undercutting is particularly bothersome because it significantly reduces blade life. Even though up to half of the original material of each abrasive cutting segment may remain, the entire blade must be replaced for reasons of safety. That is, if an undercut cutting segment breaks loose during use due to lack of core support, an undesirable condition results. Moreover, since the abrasive cutting segments are the most costly portion of the blade, significant economic loss is incurred by undercutting due to nonuse or waste of the remaining cutting segment material. In addition, frequent replacement of undercut blades further reduces productivity by increasing the down time spent replacing the blades.
Undercutting is particularly acute when "green" concrete is being cut. Green concrete is concrete in its relatively freshly poured state prior to curing. Curing or setting up can take from 4 to 60 hours to complete. During this time, the green concrete begins to shrink. If this shrinkage is not controlled, cracks will form throughout the concrete. In order to avoid this uncontrolled cracking, the green concrete must be cut or grooved to provide stress relief. These cuts and grooves are commonly referred to as contraction joints.
In practice, it is often difficult to accurately determine exactly when a particular pour of concrete has sufficiently cured to begin cutting. If a saw operator waits too long, excessive stresses will build up and cause cracking of the concrete. However, if the saw operator does not wait long enough, and excessive undercutting will result.
That is, if the green concrete is not sufficiently cured or set up prior to cutting, conventional cutting segments will pull or tear the sand and rock particles from the concrete matrix rather than cutting through or shearing these particles. This is known as spalling. When this occurs, a particularly acute undercutting condition results where relatively large quantities of abrasive sand and rock particles are forced into contact with the blade core.
At the same time, a ragged unsightly cut is produced due to the pulling and tearing of the rock and sand particles from the edges of the cut. This condition is known as raveling. Raveling is most pronounced when "aggressive" blades are used having wide gullets which allow the cutting segments to take large bites from the concrete.
Another drawback experienced with conventional segmented blades is the generation of excessive vibration. This vibration is frequently accompanied by high operating noise levels. An associated condition which accompanies blade vibration is a bucking or jerking of the blade away from the cutting surface. This reduces cutting rate, extends cutting time and is extremely annoying to the operator of the saw.
As the blade vibrates, its contact with the material being cut is disrupted. This intermittent contact prevents continuous cutting and thereby decreases cutting efficiency by increasing the time required to complete a given cut. Moreover, blade vibration increases the rate of cutting segment wear as the cutting segments intermittently hammer and pound against the material being cut. This type of intermittent impact causes rapid segment deterioration and wear.
Prior attempts to reduce undercutting by incorporating one or more radially recessed cutting elements between the remaining cutting elements resulted in increased blade vibration and wear. That is, the relatively large circumferential gap created by each recessed cutting element and the adjacent gullets results in a significant lack of circumferential contact between the material being cut and the remaining cutting elements. This condition creates a radially and circumferentially directed impulse on the leading face of the next cutting element as it enters the cut. In effect, the large gap created by prior radially recessed cutting elements allows the blade to "fall down" into the cut and requires the next cutting element to "lift up" the blade to continue cutting.
Accordingly, a need exists for a segmented type blade which reduces vibration, reduces undercutting and raveling and which allows for full use of the abrasive cutting segments by preventing premature wear adjacent the bond line formed between the blade core and the cutting segments.